c# 怎么实现窗体的任意拖动？

Question

现有一个Form 
添加一个picturebox 设置为dock=fill
鼠标点击picturebox实现窗体的拖动该怎么做？
注意：
下面这个函数已经不管用了，因为picturebox已经覆盖了form
  protected override void WndProc(ref System.Windows.Forms.Message m)
        {
            switch (m.Msg)
            {
                case WM_NCHITTEST:
                    base.WndProc(ref m);
                    if (m.Result == (IntPtr)HTCLIENT)
                    {
                        m.Result = (IntPtr)HTCAPTION;
                    }
                    break;
                default:
                    base.WndProc(ref m);
                    break;
            }
        }[/color]

Answer 1

        private Point mouseOffset;
        private bool isMouseDown = false;        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                mouseOffset = new Point(-e.X, -e.Y);
                isMouseDown = true;
            }
        }        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (isMouseDown)
            {
                Point mousePos = Control.MousePosition;
                mousePos.Offset(mouseOffset.X, mouseOffset.Y);
                this.Location = mousePos;
            }
        }        private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                isMouseDown = false;
            }
        }

Answer 2

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        [DllImport("user32.dll", EntryPoint = "SendMessage")]
        public static extern int SendMessage(IntPtr hWnd, int wMsg, int wParam, int lParam);
        [DllImport("user32.dll", EntryPoint = "ReleaseCapture")]
        public static extern int ReleaseCapture();
        public const int WM_SysCommand = 0x0112;
        public const int SC_MOVE = 0xF012;
       
    
       
        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            ReleaseCapture();
            SendMessage(this.Handle, WM_SysCommand, SC_MOVE,0 );
        }
    }
}